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HEAVY  OILS  (LUBRICATING OILS)                   351

2.  Specific Gravity.—Determined as with crude petroleum.

3.  Distillation.—The flasks used for crude petroleum are employed.
The temperature at which the distillation commences is noted and the
distillate up to 300 -310°, representing the light oils and illuminating oil,
collected and weighed.

For fiscal purposes (in Italy), the procedure followed is that indicated under
Crude petroleum, 2. When decomposition occurs, recourse is had to distillation
under reduced pressure, as indicated later for residues.

4.  Volatility.—When heated, heavy oils begin to emit vapour at a
certain point.    To determine the quantities of the oil evaporating in a
certain tune at different temperatures, in accordance with the^conditions
laid down in contracts, the following procedure  (Holde) is employed:
The oil-container A of the Pensky-Martens apparatus (Fig. 47) is charged to
the mark with the oil and weighed.    It is then heated for the prescribed
tune ; for temperatures between 100° and 200°, a glycerine bath is used,
but for higher  temperatures (200-300°) a bath of a heavy cylinder oil
having a flash point above 300° is employed.

The temperature of the oil is measured by means of a thermometer from
which the adhering oil is removed by a piece of filter-paper (previously
weighed with the crucible), which is added to the oil. After the experiment,
the oil-contained is cooled in water, dried, left in a desiccator for about 30
minutes and weighed ; the loss in weight gives the volatile oil.

With temperatures higher than 300°, the oil may be heated directly
in the Pensky-Martens apparatus.

5.  Flash Point.—This is determined for heavy oils in the Pensky-
Martens apparatus (Fig. 47).   The upper view shows a section of the essen-
tial parts of the apparatus.    A is a brass cylinder similar to that of the
Abel apparatus and is fitted with a level gauge and a vaned stirrer a ; it
is placed inside an iron envelope B with very thick walls.   This part of
the apparatus is surrounded and protected from radiation by a cupola-
shaped brass mantle and is heated by means of a triple burner C, a wire
gauze R being interposed.    The cover of the vessel A carries a thermometer
t usually graduated from about 80° to 250°, with its bulb dipping into the
liquid, and a gas flame / which is brought near to a small window and the
latter at the same time opened by turning a knob b.   A fixed flame I serves
to re-light the movable flame when this is extinguished by the explosion.
All the dimensions of the apparatus are fixed exactly.

The oil (previously dehydrated with calcium chloride if it contains
water) is placed in the vessel A and the apparatus heated to 80°, after
which the stirrer is started and the flame regulated so that the temperature
rises about 5° per minute. Observations are made firstly at intervals of
2°, but when the elongation of the flame indicates the proximity of the
flash point, at each degree. The results of several experiments made with
the same oil do not as a rule differ by more than 2° or 3° among themselves.

A simpler but less exact method of finding the flash point of a heavy
oil consists in heating the latter in a porcelain crucible 4 cm. in height and
width, which is filled to within i cm. from the top and furnished with antain more than